1. Field of the Invention
The present invention generally relates to fluid coupling devices, and more particularly to a torque converter for hybrid vehicles having a one-way clutch for a turbine wheel, and a method for making the same.
2. Background of the Invention
Currently, the demand for “clean” vehicles has a tendency to increase as a result of the need to reduce fuel consumption and limit pollution. In general, hybrid systems are being developed for the purpose of achieving the aforementioned needs. Hybrid vehicles are known, for example, for having a torque converter and recuperative braking, wherein an alternator (or generator) is used to collect kinetic energy during braking of the vehicle. The alternator converts this collected kinetic energy into electrical energy, in order to charge an energy storage device in the form for example of a pack of super-capacitors or a battery. This energy, which is recuperated, is then returned to the various items of electrical and electronic equipment, which the motor vehicle includes. The electrical energy can also be used to start the thermal engine, or to assist the torque of the thermal engine.
In some operating conditions of a hybrid vehicle, such as in coasting mode, engine braking mode and regeneration mode, an output hub for a torque converter rotates faster than the turbine wheel of the torque converter. Typically, the output hub and turbine wheel are non-rotationally connected. Thus, during the coasting, engine braking and regeneration modes, the rotation of the turbine wheel reverses the typical fluid flow patterns in the converter and the turbine “pumps” fluid to the impeller wheel. Such operation of the turbine wheel is undesirable because the rotation of the turbine wheel heats the oil in the torque converter, resulting in excessive heat losses and, in some cases, even damage to the torque converter.
Moreover, during coasting of a hybrid vehicle, drag caused by a turbine wheel of the torque converter decreases efficiency of an electric motor of the hybrid vehicle as the drag creates a reverse torque and reduces the effective torque of the electric motor.
Also, in some operating conditions, such as regeneration mode in a hybrid vehicle, it is desirable to prevent rotation of the associated internal combustion engine. Furthermore, rotation of the turbine wheel can transfer some torque to the impeller wheel, and then to the internal combustion engine. It is known to use mechanical devices, such as one-way clutches or gear mechanisms, to disconnect an input shaft from the torque associated with the regeneration mode.
While conventional hydrokinetic torque-coupling devices, including but not limited to those discussed above, have proven to be acceptable for application in hybrid vehicles, improvements in one-way clutches allowing the turbine wheel of torque converters used with hybrid vehicles to be disconnected from the transmission input shaft during regeneration mode, that may enhance their performance and cost, are possible.